(1) Field Of Invention
The present invention relates to suppressing the formation and/or growth of a corner vortex of the type formed in a moving fluid passing across structural surfaces at the juncture formed by mutually intersecting surfaces of the structure.
(2) Description of the Prior Art
One of the interesting problems in fluid dynamics is the study of corner vortex. A corner vortex develops or exists at a corner formed by two intersecting flat or curved surfaces. It has a secondary cross-stream flow. It can be a system of several vertices. Wind tunnel tests have shown that a corner vortex produces a three dimensional flow which is undesirable. The corner vortex is produced by a lateral instability mechanism as shown for example in the textbook entitled "The Structure of Turbulent Shear Flow" by A. A. Townsend, Page 331, published by Cambridge University Press, Cambridge, U. K. in 1976, Second Edition. Such theoretical analysis shows that wavelengths up to four boundary layer thicknesses have the potential to grow. That is, the vortex becomes progressively more of a problem as the fluid flows along the corner because as the vortex moves downstream it strengthens causing more drag, turbulence, noise and a long wake as a result.
While vortex generators have been found useful in some applications they depend upon creating a vortex to alleviate problems inherent in a region of fluid flow where separation of the fluid from an underlying surface can be expected to occur. Such vortex generators themselves create large flow separations and have a high degree of drag as discussed in references such as "Vortex Unwinding in a Turbulent Boundary Layer", C. B. McGinley and G. B. Beeler, AIAA Journal of Aircraft, 1987, Vol. 24, No. 3, Pages 221-222.The present invention seeks to alleviate the flow separation caused by a corner vortex at the juncture between mutually intersecting structural surfaces either in a wind tunnel or on an aircraft or water craft.
Examples of prior art patents that disclose various vortex generating devices designed to alleviate the separation of fluid flow from an underlying surface can be summarized as follows:
U.S. Pat. No. 4,378,922 illustrates in FIG. 2 a series of longitudinally spaced fins projecting laterally beyond the surfaces of the forward portion of a fuselage or hull structure. These fins generate small vortices at angles of attack where the fuselage itself might tend to generate unpredictable vortices and thereby cause adverse yawing effects on the fuselage.
U.S. Pat. No. 4,429,843 illustrates in FIG. 1 a plurality of projecting fingers 30, 30 provided adjacent the upper surface of an airfoil and oriented in the direction of fluid flow so as to create vortices rotating in opposite directions at the juncture between the inside surface of the fingers and the upper surface of the airfoil. These devices are intended to enhance the lifting capability of the wing presumably by forestalling flow separation of the airfoil across the upper surface at higher angles of attack.
U.S. Pat. No. 4,836,473 suggests both boundary layer suction devices and vortex generators 11, 11 which operate in cooperation with one another to reduce the drag across various structural portions of an aircraft where flow separation is likely to occur.
U.S. Pat. No. 4,863,121 teaches the use of flow aligned riblets of specific geometry that are designed to reduce drag by modifying the turbulent boundary layer. The height of these riblets is related to the boundary layer thickness.
Finally, U.S. Pat. No. 4,697,769 discloses a method for controlling vortices along the leading edges of a delta wing by creating a small disturbance in one or both of the leading edges to alter the lift otherwise produced by the wing so as to create a more uniform vortex along each of the two leading edges of the wing or to actually create a rolling moment by disturbing one leading edge vortex and not the other.
These prior art patents do not show or suggest how to reduce the adverse effects of a corner vortex at the juncture between mutually intersecting structural surfaces either in a wind tunnel test section or on an aircraft or watercraft where the hull or fuselage has a projection such as a wing that creates a corner where propagation of a corner vortex can disrupt the flow of fluid along such corner.